How do organic solvents affect peroxidase structure and function?

The effect of organic solvents on horseradish peroxidase structure and function has been studied. Some, but not complete, enzyme denaturation occurs even in low volumes of water-miscible organic solvents (e.g., greater than 30% v/v dioxane, greater than 50% v/v methanol, and greater than 20% v/v acetonitrile) as determined by the decreased difference between the fluorescence of peroxidase's sole tryptophan residue and free L-tryptophan in solution. Absorbance and electron paramagnetic resonance spectroscopies indicate exposure of peroxidase's active site to the organic solvent. This reduces the local polarity in the enzyme's active site and results in stronger hydrogen bonding of phenolic substrates to the enzyme. In extreme cases (e.g., 95% v/v dioxane, 90% v/v acetonitrile, and ethyl and butyl acetate containing 2 and 1% v/v aqueous buffer, respectively), the transition state of the enzymic reaction is sufficiently perturbed so as to alter the magnitude of the Hammett rho value. This is most likely the result of the increased strength of hydrogen bonding between electron-donating alkoxyphenols (negative sigma values) and an electrophilic group in the enzyme's active site, thereby reducing catalytic efficiencies for such substrates relative to alkyl- and chlorophenols. Perhaps the most important effect of the organic solvent, however, is the significant ground-state stabilization of phenolic substrates in organic media as opposed to aqueous buffer. This stabilization can account for nearly 4 orders of magnitude in reduction of catalytic efficiency and is manifested in increased Km's. This study indicates that enzymes can maintain much of their native active-site structure in organic media and that the effect of solvent on substrate thermodynamics must be considered.     

Enzymatic synthesis of tea theaflavin derivatives and their anti-inflammatory and cytotoxic activities

Derivatives based on a benzotropolone skeleton (9-26) have been prepared by the enzymatic coupling (horseradish peroxidase/H2O2) of selected pairs of compounds (1-8), one with a vic-trihydroxyphenyl moiety, and the other with an ortho-dihydroxyphenyl structure. Some of these compounds have been found to inhibit TPA-induced mice ear edema, nitric oxide (NO) synthesis, and arachidonic acid release by LPS-stimulated RAW 264.7 cells. Their cytotoxic activities against KYSE 150 and 510 human esophageal squamous cell carcinoma and HT 29 human colon cancer cells were also evaluated.     

Molecular Characterization of Korean Bacillus anthracis Isolates by Amplified Fragment Length Polymorphism Analysis and Multilocus Variable-Number Tandem Repeat Analysis

We analyzed the genetic relationships and molecular characteristics of 34 Bacillus anthracis isolates from soil and clinical samples in various regions of Korea and 17 related Bacillus species, using the amplified fragment length polymorphism (AFLP) and multilocus variable-number tandem repeat (MLVA) approaches. Triplicate AFLP profiles of these strains showed high reproducibility and identified 376 polymorphisms. AFLP phylogenetic analysis of B. anthracis isolates showed a high level of similarity, 0.93, and this monomorphic fragment profile proved to be useful to differentiate B. anthracis strains from other Bacillus species. The B. cereus group was separated from other Bacillus species at a level of similarity of 0.68. Among them, some B. cereus strains showed genetic interspersion with B. thuringiensis strains. The evolutionary pattern of nucleotide differences among B. anthracis strains with the eight MLVA markers showed nine MLVA types. Three MLVA types, M1 to M3, were pathogenic B. anthracis isolates and were assigned as new genotypes belonging to the A4 and B3 clusters, compared with 89 genotypes deduced from previous data. This indicates that differences in cluster prevalence and distribution may be influenced more by MLVA markers on two plasmids loci and human activity. Consequently, we suggest that the novel MLVA type may represent significant evidence for historic adaptation to environmental conditions of the Asian continent, particularly Korea. Therefore, MLVA techniques may be available for molecular monitoring on anthrax-release-related bioterrorism and further study is required for the continuous epidemiological study of variable anthrax collections.     

Molecular chaperone GRP78/BiP interacts with the large surface protein of hepatitis B virus in vitro and in vivo

The proper folding and assembly of viral envelope proteins are mediated by host chaperones. In this study, we demonstrated that an endoplasmic reticulum luminal chaperone GRP78/BiP bound specifically to the pre-S1 domain of the L protein in vitro and in vivo where complete viral particles were secreted, suggesting that GRP78/BiP plays an essential role in the proper folding of the L protein and/or assembly of viral envelope proteins.     

Targeted delivery of a phosphopeptide prodrug inhibits the proliferation of a human glioma cell line

Peptides are ideal candidates for developing therapeutics. Polo-like kinase 1 is an important regulatory protein in the cell cycle and contains a C-terminal polo-box domain, which is the hallmark of this protein family. We developed a peptide inhibitor of polo-like kinase 1 that targets its polo-box domain. This new phosphopeptide, cRGDyK-S-S-CPLHSpT, preferentially penetrates the cancer cell membrane mediated by the integrin receptor, which is expressed at high levels by cancer cells. In the present study, using high performance liquid chromatography and mass spectroscopy, we determined the stability of cRGDyK-S-S-CPLHSpT and its cleavage by glutathione under typical conditions for cell culture. We further assessed the ability of the peptide to inhibit the proliferation of the U87MG glioma cell line. The phosphorylated peptide was stable, and the disulfide bond of cRGDyK-S-S-CPLHSpT was cleaved in 50 mM glutathione. This peptide inhibited the growth of cancer cells and changed their morphology. Therefore, we conclude that the phosphopeptide shows promise as a prodrug and has a high potential to act as an anticancer agent by inhibiting polo-like kinase 1 by binding its polo-box domain. These findings indicate the therapeutic potential of PLHSpT and peptides similarly targeted to surface receptors of cancer cells and to the functional domains of regulatory proteins.     

Structural insight into receptor-selectivity for lurasidone

Lurasidone is a novel antipsychotic agent with high affinity for dopamine D₂, 5-hydroxyltryptamine 5-HT_2A, and 5-HT₇ receptors. Lurasidone has negligible affinity for histamine H₁ and muscarinic M₁ receptors, which are thought to contribute to side effects such as weight gain, sedation, and worsening of cognitive deficits. Our interests focus on why lurasidone has such high selectivity for only a part of these aminergic G-protein coupled receptors (GPCRs) and the different binding profile from ziprasidone, which has the same benzisothiazolylpiperazine moiety as lurasidone. In order to address these issues, we constructed structural models of lurasidone–GPCR complexes by homology modeling of receptors, exhaustive docking of ligand, and molecular dynamics simulation-based refinement of complexes. This computational study gave reliable structural models for D₂, 5-HT_2A, and 5-HT₇, which had overall structural complementarities with a salt bridge anchor at the center of the lurasidone molecule, but not for H₁ and M₁ owing to steric hindrance between the norbornane-2,3-dicarboximide and/or cyclohexane part of lurasidone and both receptors. By comparison with the structural models of olanzapine–GPCRs and ziprasidone–GPCRs constructed using the same computational protocols, it was suggested that the bulkiness of the norbornane-2,3-dicarboximide part and the rigidity and the bulkiness of the cyclohexyl linker gave lurasidone high selectivity for the desired aminergic GPCRs. Finally, this structural insight was validated by a binding experiment of the novel benzisothiazolylpiperazine derivatives. This knowledge on the structural mechanism behind the receptor selectivity should help to design new antipsychotic agents with preferable binding profiles, and the established computational protocols realize virtual screening and structure-based drug design for other central nervous system drugs with desired selectivity for multiple targets.     

Serum Wisteria Floribunda Agglutinin-Positive Mac-2 Binding Protein Values Predict the Development of Hepatocellular Carcinoma among Patients with Chronic Hepatitis C after Sustained Virological Response

Measurement of Wisteria floribunda agglutinin-positive human Mac-2 binding protein (WFA⁺-M2BP) in serum was recently shown to be a noninvasive method to assess liver fibrosis. The aim of this study was to evaluate the utility of serum WFA⁺-M2BP values to predict the development of hepatocellular carcinoma (HCC) in patients who achieved a sustained virological response (SVR) by interferon treatment. For this purpose, we retrospectively analyzed 238 patients with SVR who were treated with interferon in our department. Serum WFA⁺-M2BP values were measured at pre-treatment (pre-Tx), post-treatment (24 weeks after completion of interferon; post-Tx), the time of HCC diagnosis, and the last clinical visit. Of 238 patients with SVR, HCC developed in 16 (6.8%) patients. The average follow-up period was 9.1 years. The cumulative incidence of HCC was 3.4% at 5 years and 7.5% at 10 years. The median pre-Tx and post-Tx WFA⁺-M2BP values were 1.69 (range: 0.28 to 12.04 cutoff index (COI)) and 0.80 (range: 0.17 to 5.29 COI), respectively. The WFA⁺-M2BP values decreased significantly after SVR (P < 0.001). The median post-Tx WFA⁺-M2BP value in patients who developed HCC was significantly higher than that in patients who did not (P < 0.01). Multivariate analysis disclosed that age (> 60 years), sex (male), pre-Tx platelet count (< 15.0×10³/μL), and post-Tx WFA⁺-M2BP (> 2.0 COI) were associated with the development of HCC after SVR.

Conclusion

Post-Tx WFA⁺-M2BP (> 2.0 COI) is associated with the risk for development of HCC among patients with SVR. The WFA⁺-M2BP values could be a new predictor for HCC after SVR.     

Linking two DNA duplexes with a rigid linker for DNA nanotechnology

DNA has recently emerged as a promising material for the construction of nanosized architectures. Chemically modified DNA has been suggested to be an important component of such architectural building blocks. We have designed and synthesized a novel H-shaped DNA oligonucleotide dimer that is cross-linked with a structurally rigid linker composed of phenylene and ethynylene groups. A rotatable DNA unit was constructed through the self-assembly of this H-shaped DNA component and two complementary DNA oligonucleotides. In addition to the rotatable unit, a locked DNA unit containing two H-shaped DNA components was also constructed. As an example of an extended locked structure, a hexagonal DNA origami dimer and oligomer were constructed by using H-shaped DNA as linkers.